Breeding of Escherichia coli by Ion Beam Mutagenesis Combined with RQ On-line Regulation for High-Efficient Production of Polysialic Acid

Escherichia coli ATCC13027 is a strain capable of producing polysialic acid (PSA). In order to put it into industrial application, strain mutagenesis combined with optimization of the fermentation process was used to increase the PSA yield. Firstly, low energy nitrogen ion beam injection was performed to obtain different strains with varied PSA yields and three different strains were chosen out. Then the respiration quotient (RQ) curves of the three strains were compared during the fermentation process. Finally, a strategy for feeding corn steep powder (CSP) was formulated based on the effect of pulsed feeding of CSP on the RQ. Results showed that the highest PSA titer attained was 3.94 g/L, which was increased by 36.81% as compared with that of the wild strain when the ion beam dose was set as 10 × 1014 ion/cm2. The RQ value of the strain with the highest yield was the lowest during the rapid synthesis phase of PSA. Considering that pulsed feeding of CSP had a significant effect on RQ (P < 0.01), CSP was fed starting from 16 h to control RQ around 0.8 in a 50 L fermentor and as a result, PSA titer reached 12.83 g/L, which was 45.30% and 88.95% higher than that of the control and the original strain, respectively. The high PSA yield strain and the strategy of real-time online regulation for PSA production presented in this study provide theoretical support for PSA industrialization.